WEST LAFAYETTE, Ind. - The beneficial compounds in green tea powders aren't as stable as once thought, according to a Purdue University study that will give industry guidelines on how to better store those powders.
"People drink green tea for health benefits, so they want the catechins to be present," said Lisa Mauer, a professor of food science. "The instant powder beverages are becoming more popular for consumers, and it's important to know how storage can influence nutrition of your products."
Catechins are the source of antioxidants thought to fight heart disease, cancer, diabetes and other health problems. Green tea powders are often used as ingredients in products that are flavored like green tea or tout the health benefits of the tea. U.S. imports of green tea increased more than 600 percent from 1998 to 2007, according to the U.S. Department of Agriculture.
Mauer found that increased temperature ╨ and humidity, to a smaller degree ╨ speed catechin degradation. She said it had been believed that the powders were stable below the glass transition temperature, the temperature at which an amorphous solid changes from a rigid, glassy state to a rubbery, viscous state. In that rubbery state, compounds may start reacting with each other faster due to increased molecular mobility, leading to significant chemical degradation.
But Mauer's findings, reported in the early online version of the Journal of Agricultural and Food Chemistry, showed that green tea powder degrades at lower temperatures, even below the glass transition temperature.
"Tea powders are not infinitely stable below their glass transition temperature. They degrade more slowly below that temperature, but they can still degrade," Mauer said.
Catechin concentrations were tracked using high-performance liquid chromatography. The method involved dissolving the green tea powder into a solution, which then passed through a column. C
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